I built a a simple tracker in the mid-80's using 5 small, matched solar cells, voltage comparators and two shading strips. I forget how the motors were driven, just that it wasn't very pretty and it used dual battery packs. It worked really well, though.

I've also seen a cone shaped design which had 4 parallel holes with CdS cells at the bottom and a reference cell at the tip.

Have fun making the circuit and entering the program. I hope the focus of the device shifts to its multiplexing purpose. Everyone is focused on the solar application, but the sensors can be anything.

The program compares TWO banks (vertical and horizontal) of 30 analog sensors EACH. It uses one-byte precision or a maximum of 256 digital values. 256 divided by 30 sensors gives approximately 1 in 8 chance of two sensors having the same value. If you modify the PIC program to sense all 64 possible switches of the MUX into one pin of the MCU, you should consider right justifying the bits to get 10 bits of precision or 1024 values. This involves modifying the code at comments provided in the code. Contact me with any questions.

Yep, the analog quad cell / baffle arrangement worked well for detection but in a purely analog system, the servo motors were always being tickled. Digital lets you add hysteresis, averaging and any other sort of condition mediation you'd like. It's also stepper friendly. It works pretty well here in Hawai'i but I did much of my tracker work in Seattle, land of grey skies.

Everyone usually manages to settle on a solution that works for their situation ( cost, available parts, space, time, etc.. ) It's fun to learn from the diversity.

At 40-60K$ for a home PV system, I want to see every watt I can possibly get. I wonder if the contractor panels have to be marked" this side up"?

Nice work, Jerald. What I find interesting about your design is that it uses a solution that a human brain would use. No human would calculate the sun's position in order to find it quickly. Asking, "where's the sun?" should work for machines, too.

Nancy, I agree this is a great project. PIC processors are used a lot of places. I have played around with their development kits. It's always nice to see/read about the different projects people develop.

@kf2qd: You probably never measured the output of a solar panel when a cloud appears. It is simply actually - the output power is linear with the amount of light.

Since it does not get pitch dark when a cloud appears, the solar panel does not stop delivering power. It may be half the amount and on very severely overcast (dreadful dark grey rainy days as there are in The Netherlands) the output may be in the order of 10%, but they still deliver power.

Since the tracker should consume a minuscule amount of power, it has a very large gear reduction since it does not move fast, so it can be powered by a small motor and even that motor needs to operation only part time, there is no reason to stop tracking when "the sun disappears" behind a cloud. The power consumed by the tracker should be in the order of 1% of the array output and it has the potential to double the daily energy output - depending on latitude and shadowing.

At the end of the day the panels are typically parked in more or less horizontal position anyway, which is safety in case a storm comes at night.

Note that the tracker will not lose the sun even when it is clouded for a long time, since the sun has a predictable path. So, as long as you do not completely reset your tracker and it has either a clock or knowledge of the previus sun position it can continue to point the panels to the correct position even when it has no good measurements for some time (or ever - it may be completely based on time and latitude to calculate the sun position).

I wonder why so many sensors were used. I know that it is in theory possible to make a tracker with a single photo sensor, but the simplest systems I have seen always use two pairs of sensors, one in X and one in Y direction to find the sun when starting from any orientation.

It's me, the author again. Does anyone have a good circuit for Gadget Freak that finds the sun with analog comparators? I tried using several op amp comparators all voting on who had the brightest signal. It didn't work very well. Show me where I went wrong. Maybe you used your method for some other purpose.

A few weeks ago, Ford Motor Co. quietly announced that it was rolling out a new wrinkle to the powerful safety feature called stability control, adding even more lifesaving potential to a technology that has already been very successful.

It won't be too much longer and hardware design, as we used to know it, will be remembered alongside the slide rule and the Karnaugh map. You will need to move beyond those familiar bits and bytes into the new world of software centric design.

People who want to take advantage of solar energy in their homes no longer need to install a bolt-on solar-panel system atop their houses -- they can integrate solar-energy-harvesting shingles directing into an existing or new roof instead.

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